Lubricant compositions

ABSTRACT

A lubricant composition for a high load carrying oil comprises a synergistic mixture of a neutral alkyl phosphorus compound and a sulphur carrier. The neutral alkyl phosphorus compound is selected from neutral alkyl and alkoxyalkyl phosphates, phosphonates, phosphinates and phosphites. Preferred neutral alkyl phosphorus compounds are triisobutyl phosphate, tributoxyethyl phosphate and dioctyl octyl phosphonate. Preferred sulphur carriers are sulphurised fatty acid esters and dialkyl polysulphides. High load carrying oils containing the lubricant composition of the invention include metal working fluids, gear oils, extreme pressure turbine oils and hydraulic oils.

This invention relates to novel lubricant compositions that are usefulas lubricants in high load carrying oils, e.g. metal working fluids,gear oils, extreme pressure turbine oils and hydraulic oils. Thelubricant compositions of the invention are especially useful in metalworking fluids.

The cutting of metal involves the expenditure of significant amounts ofenergy and the development of high temperatures as the cutting toolremoves metal from the workpiece. In order to reduce the energyconsumed, obtain a long life for the cutting tool and a high surfacefinish on the workpiece, it is essential that the lubricant used is ableto operate efficiently under the conditions of operation. This meansessentially that it is capable of working at very high loads and quicklyremoving the heat generated by the cutting process. Mineral oil alonedoes not have sufficient lubricity to perform this function and it isnecessary to incorporate additives to enhance this aspect of the oil'sperformance.

In the past the most common extreme pressure additives have been thosecontaining chlorine (for example C14-17 chlorinated paraffins),phosphorus containing additives in the form of neutral triarylphosphates, alkyl or alkylaryl acid phosphates and alkylpolyalkoxy oralkylarylpolyalkoxy acid phosphates and sulphur carriers (for examplesulphurised olefins, sulphurised esters, and sulphurised fats). Thelevel of performance offered by the different additives varies dependingon the temperatures at which the active species are released to form asalt layer at the metal surface. This in turn depends on the speed andfeed rate of the cutting tool, the type and hardness of the alloy beingmachined and the specific machining operation.

The severity of the application would largely determine the chemicalnature of the selected extreme pressure additive, the level of use andwhether a combination of additives might be preferable. For example, ifthe application was not too heavy duty it might use a low concentrationof an extreme pressure additive (such as a chlorinated paraffin or aphosphate ester). While for heavier duty applications, higherconcentrations of the different types of extreme pressure additives ormixtures of these additives are utilised by the formulator.

None of the commonly used extreme pressure additives is without itsdisadvantages. Sulphur can produce staining of workpieces derived fromnon-ferrous alloys at high concentrations and also an unattractive odouras the carrier decomposes to release the sulphur. Problems associatedwith the usage of chlorine stem from concerns about disposal of thecutting fluid These compounds can also produce hydrochloric acid ondecomposition which can cause corrosion of the workpiece and equipmentin the environment of the machining operation.

In addition to mineral oil as the “carrier” for the extremepressure/antiwear additives, and usually for applications which are moresevere, oil in water emulsions and water based solutions are alsocommonly used in applications which require less lubricity. However inall these fluids, additives are required to improve the lubricationperformance of the fluid.

The type of phosphorus-containing additives which are found in metalworking fluids are typically alkyl or alkylaryl acid phosphates andalkylpolyalkoxy or alkylarylpolyalkoxy acid phosphates used either asthe free acid or neutralised with basic materials such as alkanolaminesand caustic soda e.g. products sold under the trade marks of Lubrhophosand Rhodafac; neutral triaryl phosphates e.g. synthetic isopropylatedphenyl phosphates such as are available commercially under the Duradtrde mark.

Concern has been expressed regarding the use of neutral or acid aryl andacid alkylaryl phosphates lest the used fluid containing phenoliccompounds (arising largely from the hydrolysis of the phosphates) shouldescape into the environment and contaminate water courses. Acidphosphate esters can also become less effective as extreme pressureadditives when neutralised and are also unstable when subjected to hardwater.

One objective of the present invention is to provide a novel lubricantcomposition which improves the cutting performance of both neat oil andwater based cutting fluids. Another objective of the present inventionis to replace acid phosphates as extreme pressure/anti wear additives inmetal working applications. This objective has been achieved by thecombination of certain neutral alkyl phosphorus compounds with certainsulphur carriers.

According to the present invention, there is provided a lubricantcomposition for a high load carrying oil said lubricating compositioncomprising:

-   (a) a neutral alkyl phosphorus compound selected from those    corresponding to the following general formulae:-   (i) neutral alkyl phosphates-    wherein R₁, R₂ and R₃ are the same or different and are alkyl    groups with 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.-   (ii) neutral alkyl phosphonates-    wherein R₁, R₁ and R₃ have the same meaning as in I above.-   (iii) neutral alkyl phosphinates-    wherein R₁, R₂ and R₃ have the same meaning as in I above.-   (iv) neutral alkoxyalkyl phosphates-    wherein R₄, R₆ and R₈ are —C₂H₄ or C₃H₈ and R₅, R₇ and R₉ are the    same or different and are alkyl groups with 1 to 8 carbon atoms and    n is 1 to 6.-   (v) neutral alkoxyalkyl phosphonates-    wherein R₄, R₅, R₆, R₇, R₈ and R₉ and n have the same meanings as    in IV above.-   (vi) neutral alkoxyalkyl phosphinates-    wherein R₄, R₅, R₆, R₇, R₈ and R₉ and n have the same meanings as    in IV above.-   (vii) neutral alkyldialkoxyalkyl phosphonates-    wherein R₄, R₅, R₆, R₇ and n have the same meanings as in IV above    and R₁₀ is an alkyl group with 1 to 18 carbon atoms, preferably 4 to    12 carbon atoms.-   (viii) neutral dialkylalkoxyalkyl phosphinates-    wherein R₄, R₅ and n have the same meanings as in IV above and R₁₀    and R₁₁ are the same or different and are alkyl groups with 1 to 18    carbon atoms, preferably 4 to 12 carbon atoms.-   (ix) neutral alkoxyalkyl dialkyl phosphonates-    wherein R₆, R₇ and n have the same meanings as in IV above and R₁₂    and R₁₃ are the same or different and are alkyl groups with 1 to 18    carbon atoms, preferably 4 to 12 carbon atoms.-   (x) neutral dialkoxyalkylalkyl phosphinates-    wherein R₆, R₇, R₈, R₉ and n have the same meanings as in IV above    and R₁₂ is an alkyl group with 1 to 18 carbon atoms, preferably 4 to    12 carbon atoms.-   (xi) neutral dialkylalkoxyalkyl phosphates-    wherein R₂ and R₃ are the same as in I above and R₄ and R₅ are the    same as in IV above.-   (xii) neutral alkyl phosphites-    wherein R₁, R₂, R₃ have the same meaning as in I above.-   (xiii) neutral alkoxyalkyl phosphites-    wherein R₄, R₅, R₆, R₇, R₈, R₉ and n have the same meanings as in    IV above.-   and (b) a sulphur carrier containing active or inactive sulphur.

The lubricant composition of the invention can comprise one or more ofthe compounds of general formulae I to XIII.

Advantageously, the neutral alkyl phosphorus compound and the sulphurcarrier are utilised in a weight ratio of P to S content from 1:50 to1:1, preferably a weight ratio of 1:1 to 1:30.

Examples of compounds of the general formulae I to XIII are as follows:

-   I—triisobutyl phosphate, tributyl phosphate, triisopropyl phosphate,    trioctyl phosphate and tri-2-ethylhexyl phosphate-   II—butyl dibutyl phosphonate and octyl dioctyl phosphonate-   III—dioctyl octyl phosphinate-   IV—tributoxyethyl phosphate-   V—butoxyethyl dibutoxyethyl phosphonate-   VI—dibutoxyethyl butoxyethyl phosphinate-   VII—octyl dibutoxyethyl phosphonate-   VIII—dioctyl butoxyethyl phosphinate-   IX—butoxyethyl dioctyl phosphonate-   X—dibutoxyethyl octyl phosphinate-   XI—butoxyethyl dioctyl phosphate-   XII—trilauryl phosphite, trioleyl phosphite, trioctyl phosphite and    tributyl phosphite-   XIII—tributoxyethyl phosphite

Preferred sulphur carriers are selected from at least one of sulphurisedsynthetic esters, sulphurised hydrocarbons (e.g. sulphurised olefins),sulphurised vegetable oils and fats, metal sulphonates, metaldialkyldithiophosphates and triaryl phosphorothionates.

The sulphur carriers serve to release sulphur at the cutting face of theworkpiece where it reacts to form a lubricating film at relatively hightemperatures.

The present invention is also a high load carrying oil which contains alubricant composition as described above.

The high load carrying oil may be a metal working fluid, a gear oil, anextreme pressure turbine oil or a hydraulic oil.

From another aspect, the present invention is also a method for workingmetal comprising (a) contacting a metal workpiece with a lubricantcomposition as described above and (b) working the metal workpiece.

The lubricant composition of the invention can include other componentsconventional in the art, e.g. surfactants, non-ionic alcohols.

Embodiments of the invention will now be described simply by way ofexample:

-   1) As sulphur carriers, Rhein Chemie products RC 2526 (a sulphurised    fatty acid ester with 26% total sulphur of which 15% is active) and    RC 2540 (a dialkylpentasulphide with 40% total sulphur of which 36%    is active).-   2) As an alkylpolyalkoxy acid phosphate, (mixed mono- and di-),    Lubrhophos LB400 ex Rhodia Chemicals which is based on oleyl alcohol    reacted with ethylene oxide and then the product is reacted with    phosphorus pentoxide. This product is oil soluble and recommended as    an EP additive for cutting oils.-   3) Durad TiBP which is tri-isobutyl phosphate-   4) Durad TBEP which is tributoxyethyl phosphate

Durad is a registered trade mark of Great Lakes Chemical Corporation.

In the following tests, an automatic drilling machine is used to drillholes in metal discs 40 mm thick. The holes are 18 mm deep while, foroil-based cutting fluids, the drill feeds and speeds were 0.13 mm/rev(or 156 mm/min) and 1200 rpm respectively. Tests were carried out untilthe drill failed either due to breakage or to excessive wear. Theaverage of at least duplicate test results are quoted.

(A) Drill Life Test Data on Mild Steel Using Neat Oil: DuradTiBP/Sulphur Carriers as Replacements for Chlorparaffins

The metal used was EN24T carbon steel; the drill feeds and speeds wereas indicated below and the base stock was an ISO VG 22 paraffinic oil.In this case the S/P ratio was 13:1. The formulation containing DuradTiBP is seen to be significantly more active than the chlorparaffin.Formulation (w/w) 1 2 3 TiBP 0.6 — Sulphur carrier (36.7% sulphur - allactive) 2.5 — 4.3 Chlorparaffin (40% chlorine) — 8.0 — ISO VG 22paraffinic oil 96.9 92.0 95.7 Holes drilled to failure 280 140 100(B) Drill Life Tests on Stainless Steel Using Neat Oil: A Comparisonwith Acid Phosphates

Stainless steel type 304 was used for this study. The sulphur carriersused were a 4:1 mix of a sulphurised fatty acid ester (26% total sulphurof which 15% is active) and a dialkyl polysulphide (40% total sulphur ofwhich 36% is active). The levels of sulphur and phosphorus used were1.5% and 0.5% respectively giving an S/P ratio of 3:1. As for previoustests the oil used was an ISO VG 22 Group 1 base. Formulations (w/w) 4 56 7 Sulphur carriers 5.2 5.2 5.2 5.2 Durad TiBP — 4.17 — — Durad TBEP —— 6.4 — Oleyl acid phosphate — — — 10.0 Neat Oil 94.8 90.63 68.4 84.8Holes drilled to failure 84 432 >>500 18

The quality of swarf associated with Durad TBEP in the above test wasregarded as excellent throughout. In fact no drill failures occurredwith this formulation.

(C) Performance of S/P Combinations on Stainless Steel UsingMacro-Emulsions

The conditions for this test were somewhat different. In order tosatisfactorily machine the stainless steel with the emulsion theconditions were modified to a feed rate of 70 mm/min and a speed of 700rpm-slightly more severe conditions than were recommended by the drillmanufacturers. The same sulphur carriers were used as in the previoustest on stainless. A concentrate of the phosphate and sulphur carrierswith emulsifiers, corrosion inhibitors, antifoams etc was first preparedin aqueous solution with the part addition of the triethanolamine base.This concentrate was subsequently added to a 60 solvent pale oil(naphthenic type) containing a further small amount of emulsifier andtriethanolamine to produce an emulsion concentrate. This emulsionconcentrate was then diluted to 4% to produce the working fluid. Tapwater with a hardness of 160 ppm calcium carbonate was used throughout.In this test, the concentration of the sulphur and phosphorus in thefinal emulsion were 0.36% sulphur and 0.012% phosphorus (a 30:1 ratio).The table below gives the approximate formulation of the concentratebefore dilution. Formulation (%) 8 9 Sulphur carriers 3.12 3.12 DuradTiBP — 0.25 Emulsifier/inhibitor mixture 2.84 4.99 Triethanolamine 3.043.04 Mineral oil 46.0 46.0 Water 45.0 42.6 Holes drilled to failure 214>>500

In this test Durad TiBP is seen to be a most effective additive which incombination with the sulphur carriers shows a significant improvementover the sulphur carriers alone.

(D) Drill Life Test Data on Stainless Steel Using Neat Oil: A Comparisonof Tributoxyethyl phosphate (TBEP) with Dioctyl octyl phosphonate

The sulphur carriers used RC2526 and RC2540 were the same as used in theprevious Examples.

Concentrations used were 1.5% sulphur and 0.5% phosphorus in an ISO VG22 paraffinic type neat oil (i.e. the same as before).

Stainless steel type 304 was used for this study.

The drill feed rate was 150 mm/min and the speed was 1500 rpm. The depthof hole was 18 mm. Formulation (w/w) Holes drilled to failure Sulphurcarriers alone  56 Sulphur carriers plus Dioctyl octyl phosphonate 336Sulphur carriers plus TBEP 500+

The above results show that although both phosphorus additives showedenhanced activity, TBEP was the higher of the two.

N.B. In the above tests, an automatic drilling machine is used to drillholes in metal discs 40 mm thick. The holes are 18 mm deep, while drillfeeds and speeds are normally 0.13 mm/rev (or 156 mm/min) and 1200 rpmrespectively. Tests were carried out until the drill failed either dueto breakage or to excessive wear. The average of at least duplicate testresults are quoted.

Although lubricity additives such as fatty oils and long chain esterscan be used in cutting fluids, these were not included in theformulations shown above.

CONCLUSIONS

A major benefit of the present invention is that neutral alkylphosphorus compounds provide a synergistic performance with sulphurcarriers in both neat oil and aqueous cutting fluids on both mild steeland stainless steel. Such a synergistic combination enables theformulation of cutting fluids with the following properties:

-   (a) no chlorine present;-   (b) the elimination of the production of phenolic degradation    products;-   (c) a possible reduction in the level of sulphur in the oil;-   (d) improved lubrication performance; and-   (e) extended drill life in metal cutting applications.

The use of neutral alkyl phosphorus compounds also allows higher levelsof phosphorus to be used when necessary. Where acid phosphates are used,the acidity effectively limits the level of phosphorus that can be usedbecause the acid can become corrosive at high levels. This allows formore flexibility in formulating mixtures of P/S and higher levels wherenecessary depending on the severity of the worling process.

Benefits from the use of the synergistic combination of the invention inapplications other than metal cutting processes include:

-   (i) An increase in the level of performance without substantially    increasing the level of the sulphur carriers. These can adversely    affect the oxidation stability and corrosive tendencies of the    formulation.-   (ii) Alternatively, for the same level of performance, it is    possible to lower the sulphur carrier level thereby favourably    impacting the stability/corrosivity of the formulation.

1. A lubricant composition for a high load carrying oil, said lubricantcomposition comprising: (a) a neutral alkyl phosphorus compound selectedfrom the group consisting of (i) a neutral alkyl phosphate of thegeneral formula I

 wherein R₁, R₂ and R₃ are the same or different and are alkyl groups of1 to 18 carbon atoms; (ii) a neutral alkoxyalkyl phosphate of thegeneral formula IV

 wherein R₄, R₆ and R₈ are —C₂H₄ or C₃H₈ and R₅, R₇ and R₉ are the sameor different and are alkyl groups of 1 to 8 carbon atoms and n is 1 to6; and (iii) a neutral dialkylalkoxyalkyl phosphate of the generalformula XI

 wherein R₂ and R₃ are the same as in formula I above and R₄ and R₅ arethe same as in formula IV above and mixtures thereof; and (b) a sulphurcarrier containing active or inactive sulphur and which is selected fromthe group consisting of sulphurised synthetic esters, sulphurisedvegetable oils and fats, metal sulphonates, dialkylpolysulphides andmixtures thereof.
 2. The lubricant composition according to claim 1wherein the neutral alkyl phosphorus compound and the sulphur carrierare present in a weight ratio of P to S content from 1:50 to 1:1.
 3. Thelubricant composition according to claim 2 wherein the neutral alkylphosphorus compound and the sulphur carrier are present in a weightratio of P to S content from 1:1 to 1:30.
 4. The lubricant compositionaccording to claim 1 wherein the phosphorus compound is selected fromthe group consisting of triisobutyl phosphate, tri-n-butyl phosphate,triisopropyl phosphate, triocyl phosphate, tri-2-ethylhexyl phosphate,tributoxyethyl phosphate, butoxyethyldioctyl phosphate and mixturesthereof.
 5. The lubricant composition according to claim 1 wherein thesulphur carrier is selected from the group consisting of a sulphurisedfatty acid, a dialkylpentasulphide and mixtures thereof.
 6. (Canceled)7. The lubricant composition according to claim 1 which is a metalworking fluid, a gear oil, an extreme pressure turbine oil or ahydraulic oil.
 8. (Canceled)
 9. The lubricant composition according toclaim 1 wherein the phosphorus compound is selected from the groupconsisting of triisobutyl phosphate, tri-n-butyl phosphate, triisopropylphosphate, triocyl phosphate, tri-2-ethylhexyl phosphate, tributoxyethylphosphate, butoxyethyldioctyl phosphate and mixtures thereof and thesulphur carrier is selected from the group consisting of a sulphurisedfatty acid, a dialkylpentasulphide and mixtures thereof.
 10. Thelubricant composition according to claim 1 further comprising one ormore additional components selected from the group consisting ofsurfactants, non-ionic alcohols and mixtures thereof.
 11. A method forworking metal comprising (a) contacting a metal workpiece with a metalworking fluid comprising an effective amount of a lubricant compositionand (b) working the metal workpiece, wherein the lubricant compositioncomprises (i) a neutral alkyl phosphorus compound selected from thegroup consisting of a neutral alkyl phosphate of the general formula I

 wherein R₁, R₂ and R₃ are the same or different and are alkyl groups of1 to 18 carbon atoms; a neutral alkoxyalkyl phosphate of the generalformula IV

 wherein R₄, R₆ and R₈ are —C₂H₄ or C₃H₈ and R₅, R₇ and R₉ are the sameor different and are alkyl groups of 1 to 8 carbon atoms and n is 1 to6; (iii) a neutral dialkylalkoxyalkyl phosphate of the general formulaXI

 wherein R₂ and R₃ are the same as in formula I above and R₄ and R₅ arethe same as in formula IV above and mixtures thereof, and (ii) a sulphurcarrier containing active or inactive sulphur and which is selected fromthe group consisting of sulphurised synthetic esters, sulphurisedvegetable oils and fats, metal sulphonates, dialkylpolysulphides andmixtures thereof.
 12. The method according to claim 11 wherein theneutral alkyl phosphorus compound and the sulphur carrier of thelubricant composition are present in a weight ratio of P to S contentfrom 1:50 to 1:1.
 13. The method according to claim 11 wherein theneutral alkyl phosphorus compound and the sulphur carrier of thelubricant composition are present in a weight ratio of P to S contentfrom 1:1 to 1:30.
 14. The method according to claim 11 wherein thephosphorus compound of the lubricant composition is selected from thegroup consisting of triisobutyl phosphate, tri-n-butyl phosphate,triisopropyl phosphate, triocyl phosphate, tri-2-ethylhexyl phosphate,tributoxyethyl phosphate, butoxyethyldioctyl phosphate and mixturesthereof.
 15. The method according to claim 11 wherein the sulphurcarrier of the lubricant composition is selected from the groupconsisting of a sulphurised fatty acid, a dialkylpentasulphide andmixtures thereof.
 16. The method according to claim 11 wherein thelubricant composition is a metal working fluid, a gear oil, an extremepressure turbine oil or a hydraulic oil.